The present invention is related to a transmission device for vehicles, including a shaft, a driven wheel with internal gear teeth defined thereon mounted to the shaft center thereof, and a small driving gear with outer gear teeth defined thereon in mesh with the internal gear teeth of the driven wheel thereof wherein the small driving gear is located at the offset center of the driven wheel therein to serve as a source of power supply. When the small driving gear, carrying the total weight and load of the vehicle, is rotated upwards at the driven wheel therein in internal offset gearing, the outer gear teeth of the small driving gear tend to climb forwards therewith along the internal gear teeth of the driven wheel thereof to rotate the driven wheel therewith, effectively converting the gravity force into dynamic driving power to reduce the output of power requirement for more economical and efficient use thereof.
Please refer to FIG. 1. A conventional transmission device of a vehicle is made up of a vehicle 10 having a shaft 11, a driven wheel 13 mounted to the outer periphery of the shaft 11 thereof, and a wheel 12 attached to the outer periphery of the driven wheel 13 thereon. In operation, the vehicle 10 is started to rotate the shaft 11 and the driven wheel 13 therewith synchronically so as to move the wheel 12 in driving motion. Meanwhile, the output of power requirement is uneconomically multiplied in the process, which makes the conventional transmission device of a vehicle rather inefficient in practical use.